Physicists discovered gravitational waves from four new black hole fusions

Enlarge / Representation of the artist from two converging black holes creating a telltale gravitation Wave signatures picked up by the LIGO / VIRGO detectors.

At a weekend workshop in Maryland, physicists from the LIGO and Virgo collaboration reported four previously unannounced discoveries of gravitational waves from black holes, including the most prominent black hole collision to date about 5 billion years ago. This merger resulted in a new black hole 80 times larger than the Sun.

All four are part of the first official catalog of gravitational wave events (so-called gravitational wave transient catalog or GWTC-1

) all events recognized so far. Their addition brings the total to 11. Two scientific papers on the new findings have been published in the sub directory of arXiv preprint (here and here).

LIGO detects gravitational waves using laser interferometry using high-power lasers Measure tiny changes in distance between objects two kilometers apart. (LIGO has detectors in Hanford, Washington, and Livingston, Louisiana.) A third detector in Italy, Advanced VIRGO, was online in 2016.) On September 14, 2015, at 5:51 CET, both detectors were the first in milliseconds Mal – direct evidence that two black holes are twisting towards each other and merging into a massive collision event that emitted strong shockwaves over space-time.

The collaboration has added two more black hole mergers from this first run. The second run, from November 30, 2016 to August 25, 2017, resulted in seven more black-hole binary mergers (including the four just-announced) and a binary neutron star fusion supported by a simultaneous gamma-ray burst and signals became the rest of the electromagnetic spectrum. It was an unprecedented recording of a major celestial event that combined light and sound, and officially marked the beginning of so-called "multi-messenger astronomy."

Enlarge / This graphic shows the masses of black holes that were previously recorded with gravitational waves.

LIGO-Virgin / Frank Elavsky / Northwestern

If the new events come from the same second runs as the previously reported events, why are we just hearing about it? That's because physicists wanted to be absolutely sure they were real detections. "We looked through the data, looked at all the features, compared them to our astrophysical predictions, compared them to monitors that showed us the condition of the instruments, whether they were present in all detectors, and our best – used, robust (but slow – running ) Supercomputer analysis codes, "wrote Shane Larsen, a Northwestern University physicist and member of the LIGO collaboration, on the Write Science blog.

All this hard work paid off with the discovery of GW170729. GW170809, GW170818 and GW170823, referring to the data on which the black holes were discovered. "By collecting events, we learn things about the Universe that you can not learn from a few observations," Larson wrote. Among other things, scientists have learned so far: The black holes that were involved in the mergers were formed from stars that were 45 times lighter than the mass of our sun. This can tell scientists something about how black holes form and grow together, which in turn can provide insights into the evolution of the stars.

The current catalog will continue to grow. LIGO and Virgo will begin the third observation run next spring, with even more sensitive instruments and improvements in data analysis techniques to detect signals in all the noise. In addition, data from all previous runs will soon be publicly available, potentially reducing even more undiscovered nuggets. "Historically, discoveries were made in archived astronomical data long after they were collected," Larson wrote. "Data is just too complex to understand, and we are too naive to do anything in the universe to detect everything in our data when we first work with it."